1. Field of the Invention
The present invention relates to a shock absorber preferably used for a suspension of a vehicle, such as an automobile.
2. Description of the Related Art
Accompanying drawing FIG. 6a is a sectional view illustrating a conventional shock absorber generally known in the art. The shock absorber in the drawing comprises a working cylinder 2 and a reservoir 5. Into the inside of the working cylinder 2, a piston 1 is slideably inserted. A rod 3 is fixed to the piston 1. Further, a piston mold 4, serving to function as a seal member, is arranged around the piston 1 so as to maintain liquid tightness with the working cylinder 2.
When external force applied by the rod 3 causes the piston 1 to move up and down (in other words, application of external force causes the working cylinder 2 to move up and down), oil moves between the inside of the working cylinder 2 and the inside of the reservoir 5 in accordance with the change in volume of the working cylinder 2. At that time, the viscosity resistance of the moving oil reduces vibration.
However, as shown in accompanying drawing FIG. 6b, a conventional shock absorber includes a piston mold 4 having a short contacting span with respect to a working cylinder 2, so that there has been a problem that possible noise (especially knock noise) generation depends on the extent of contact resistance of the piston mold 4.
Namely, in a shock absorber, contact of the piston mold 4 with the working cylinder 2 generates a drag force, which further causes a moment in the piston 1 so that a short span tends to be a cause of unstable vibration. Unstable vibration frequently results in self-induced vibration as shown in FIG. 7.